Electroplating zinc using titanium containing electrolyte



Patented July 21, 1953 ELECTROPLATING ZINC USI NG I TITANIUM CONTAINING ELECTROLYTE Raymond J .Wean, Warren, Ohio, assignor to The Wean Engineering Company, Inc., Warren, Ohio, a corporation of Ohio No Drawing. Application November 18, 1950, Serial No. 196,523

11 Claims. (01. 204-43) This invention relates to the electroplating of basis metal with zinc. ''It relates to an improved 'method of electroplating zinc on basis metal whereby a high quality product may be obtained with consistent uniformity at a rapid rate of production. The invention also comprehends a new and improved zinc-plated basis metal prodnot and especially a new and improved Zincplated ferrous metal product.

The electroplating of basis metal with zinc has been attempted and accomplished with distinct limitations for a number of years. No great difficulty is encountered in obtaining a deposit of zinc on basis metal by electroplating but serious difficulties arise in obtaining a uniform bright finish. It is possible to obtain a bright finish'by the use of organicaddition agents as I known to those skilled in the art. A wide variety of organic addition agents have been tried out; a few examples are licorice, molasses, glue, cresol, beta naphthol, resorcinol, etc. While on occasions excellent results have been obtained it has not been possible to obtain sufficiently uniform results or to accomplish the plating sufficiently fast while obtaining a uniform bright finish to make the electroplating of zinc on basis metal and particularly on ferrous metal a feasible economical commercial process when a uniform bright or lustrous finish is required. 'The organic addition agents are very diflicult' to analyze b and control. Hence it is difficult or impossible using organic addition agents to maintain "a uniform electrolyte. 'dition agents heretofore employed decompose-to form undesirable products in the electrolyte which result in'off-color plating, roughness; non uniformity of the plating so far as brightness or luster is concerned and other deleterious effects. Still further, with the use of organic addition agents brightness or luster is obtained with sacrifice of ductility; the plating produced is undesirably brittle and often sobrittle as to be completely non-commercial.

There is a great potential'market for uniform high quality bright finished basis metal electroplated with zinc, particularly ferrous metal and especially steel strip having .a uniform bright lustrous electroplated zinc coating. This has long been recognized. The electroplating process is one which adapts itself to continuous elec- A troplating of steel strip with zinc but the cost of a continuous strip electroplating line is very high and would not be justified for the continuous electroplating of steel strip coated with zinc where a uniform brightclustrous coating is re- Moreover, the organic adtitanium to the basis metal as a cathode.

quired if a more uniform and ductile bright lustrous coating than has heretofore been gobtainable in the electroplating of zinc on ferrous metal could not be regularly obtained.

I have discovered how-to produce with regu larity and rapidity zinc coated basis metal and particularly Zinc coated steel strip with the zinc coating applied by electroplating with a desirably ductile uniform bright lustrou coating so that the high cost incident to a line for continuously electroplating zinc on steel strip when such a coating is required can now be justified.

I have discovered that, contrary to the'prior concept in the art, itis'not necessary to employ in an acid electrolyte in the electroplating of zinc on basis metal organic addition agents which break down during the electroplating process with the disadvantages above'pointed out;

' I preferably do not employ any such organic addition agent. Instead of employing anaorganic addition agent which breaks down during the electroplating process I incorporate titanium in the acid electrolyte. Incorporation of titanium in the electrolyte has all the advantages without any of the disadvantages of the use of organic addition agents which break down during the electroplating process. By incorporating titanium in the electrolyte I obtain with uniformity a desirable bright lustrous finish. .I can with comparative ease maintain the electrolyte uniform. v I can obtain withuniformity :a desirably bright and lustrous and desirably ductile coating at vhigher'speed than the highest speed'at which results inferior to my results have heretofore been obtained. I provide a new Product consisting of basis metal, especially ferrous metal, electroplated With zinc in which the plating contains titanium.

I also obtain an unprecedented levelling effect on the surface of the work. The surface Of my plated work is more level than the surface of the basis metal before plating. The levelling is highly important as those skilled in the art know. Levelling is a term of art meaning decrease of surface roughness.

My method of electroplating zinc on basis ietal comprises passing an electroplating current through an electroly'tecontaining zinc and The electrolyte is preferably substantially free from organic addition agents which decompose during the electroplating. The electrolyte preferably contains at least-about .005 ounce of titanium per gallon of electrolyte. I believe that the concentration of titanium in the electrolyte should be between about .005 and about .2 ounce of titanium per gallon of electrolyte. Optium results are obtained when the electrolyte contains about .05 ounce of titanium per gallon of electrolyte.

The zinc may be introduced directly into the electrolyte or by means of an anode or both. When zinc is introduced directly into theelectrolyte either a zinciferous or a non-zinciferous anode or both may be employed. When a nonzinciferous anode is employed it may to advantage be of carbon. When a zinciferous anode is employed it may be of commercial metallic zinc anodic material. When a zinciferous anode is employed the zinc for plating may come entirely from the anode although even when using a zinciferous anode I preferably employ a substantial quantity of a source of zinc such as zinc sulphate in the electrolyte. While as above indicated I may use at the same time a zinciferous and a non-zinciferous anode I obtain excellent results using a zinciferous anode without a nonzinciferous anode. I believe that a non-zinciferous anode such 'as a carbon anode, whether used alone or with a zinciferous anode, acts to preferentially oxidize the titanium or to reduce the zinc in the electrolyte.

Desirably my electrolyte contains a titanium compound, preferably a water soluble titanium salt. I have obtained excellent results using titanous chloride. Very good results are obtainable employing an electrolyte containing a quantity of the order of .8 ounce per gallon of electrolyte of a dilute solution (of the order of 15% concentration) of titanous chloride.

I am able to employ a current density of at least about 100 amperes per square foot while obtaining excellent uniform results. As an example, I have used a current density of 180 amperes per square foot with excellent results.

I have also used much greater current densities with excellent results. Using a current density of 180 amperes per square foot I have been able to electrodeposit zinc on steel strip and uniformly obtain a lustrous bright finish, the deposit attaining a thickness of about .001" in ten minutes with appreciable levelling and good ductility. The temperature may be varied within a considerable range, higher temperature enabling the employment of high current density but with some sacrifice in finish. The time during which the electroplating is allowed to continue determines the thickness of the plating.

I find it desirable to incorporate in the electrolyte dextrose which although organic does not break down during the electroplating process. Dextrose therefore does not have the disadvantages of the organic addition agents above referred to which break down during the electroplating process. I believe that the dextrose coacts in some way with the titanium to obtain a fine grain structure in the zinc coating which is a prerequisite to a uniform lustrous finish.

Dextrose has a further advantage over the previously used organic addition agents in that it is unaffected by activated carbon. This characteristic of dextrose makes it possible to maintain or recirculate the electrolyte in contact with activated carbon to continuously remove organic contamination which may enter the electrolyte with the basis metal or otherwise. Such purification of the electrolyte has not heretofore been possible because the activated carbon would remove from the electrolyte not only the organic contaminants but also the organic addition agents which have been relied upon to obtain a bright coating.

I also find it desirable to incorporate in the electrolyte an oxidizing agent. The oxidizing agent has an oxidizing effect on the titanium in the electrolyte to maintain optimum concentration of titanium of the proper valence or valences to produce a ductile uniform bright lustrous coating. Various oxidizing agents may be employed, as, for example, hydrogen peroxide, sodium perborate, sodium peroxide, potassium permanganate and oxygen. When a carbon anode is employed oxidation of the titanium takes place at the surface of the anode. When using a zinc iferous anode without a carbon anode I preferably incorporate in the electrolyte a quantity of the order of .25 ounce of a 30% water solution of hydrogen peroxide as an oxidizing agent.

I preferably maintain relative movement between the cathode and the electrolyte. Relative movement between the cathode and the elec trolyte at a rate of the order of feet per minute produces excellent results.

Zinc may be electroplated on a wide variety of basis metals employing my invention. Basis metals most commonly electroplated with zinc in addition to ferrous metal are copper and its alloys and aluminum and its alloys.

The rate of plating is directly proportional to the current density employed in the electroplating process. High speed electroplating of zinc prior to my invention has produced a coating which has not been the desirably ductile uniform bright lustrous coating which I produce. I produce at even higher speeds and employing higher current densities than the best prior practice an unprecedented ductile uniform bright lustrous coating.

The titanium in the electrolyte does not decompose as do the organic addition agents previously employed, it desirably refines the grain size of the electrodeposited zinc whereby unprecedentedly fine uniform results are obtained at high speed with desirable levelling of the surface and with the production of a coating of zinc which is not brittle as frequently occurred when organic addition agents were used. The coatin which I obtain by electrodeposition contains a significant, though small, quantity of titanium. Normally the coating of my zinc-electroplated basis metal contains a quantity of titanium of the order of .05% to 1% of the weight of the coating.

I shall give a specific example of an aqueous electrolyte which I have used with very successful results; that electrolyte contains quantities of the order of those below indicated of the ingredients listed:

15% water solution 'ti- .8 ounce per gallon of tanous chloride. electrolyte.

When a zinciferous anode is employed without a non-zinciferous anode such as a carbon anode I preferably add to the above identified electrolyte .25 ounce of a 30% water solution of hydrogen peroxide. Using such an electrolyte at a temperature of 60 F. to 120 F. and a current density of the order of 180 amperes per square foot I have obtained regularly a uniform lustrous ductile electrodeposited zinc coating on steel strip in from 3 to minutes, the time determining the thickness of the coating.

While I have described a present preferred embodiment of the invention and. a present preferred method of practicing the same it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced Within the scope of the following claims.

I claim:

1. A method of electroplating a lustrous ductile coating of zinc on basis metal comprising passing an electroplating current from an anode to the basis metal as a cathode through an acid zinc electrolyte containing between about .005

and about .2 ounce of titanium per gallon of elec- V trolyte.

2. A method of electroplating zinc on basis metal comprising passing an electroplating current from an anode to the basis metal as a cathode through an acid zinc electrolyte substantially free from organic addition .agents which decompose during the electroplating and containing between about .005 and about .2 ounce of titanium per gallon of electrolyte.

3. 'A method of electroplating a lustrous ductile coating of zinc on ferrous metal comprising passing an electroplating current from an anode to the ferrous metal as a cathode through an acid zinc electrolyte containing between about .005 and about .2 ounce of titanium per gallon of electrolyte.

4. A method of electroplating a lustrous ductile coating of zinc on basis metal comprising passing an electroplating current from a zinciferous anode to the basis metal as a cathode through an acid zinc electrolyte containin between about .005 and about .2 ounce of titanium per gallon of electrolyte. a

5. A method of electroplating zinc on basis.

metal comprising passing an electroplating current from an anode to the basis metal as a cathode through an acid zinc electrolyte containing between about .005 and about .2 ounce of titanium per gallon of electrolyte and controlling the va-.

lence of the titanium to produce a lustrous ductile coating.

6. A method of electroplating Zinc on basis metal comprising passing an electroplating current from an anode to the basis metal as a oath-.- ode through an acid zinc electrolyte containing between about .005 and about .2 ounce of titanium per gallon of electrolyte and oxidizing the titanium to produce a lustrous ductile coating.

'7. A method of electroplating a lustrous ductile coatin of zinc on basis metal comprising passing an electroplating current from an anode to the basis metal as a cathode through an acid zinc electrolyte containing hydrogen peroxide and between about .005 and about .2 ounce of titanium per gallon of electrolyte.-

8. A method of electroplating a lustrous ductile coating of zinc on basis metal comprising passing an electroplating current from an anode to the basis metal as a cathode through an acid zinc electrolyte containing titanium chloride insuch quantity that the electrolyte contains between about .005 and about .2 ounce of titanium per gallonof electrolyte.

9. A method of electroplating zinc on basis 6 metal comprising passing an electroplating current from an anode to the basis metal as a cathode through an electrolyte containing about the quantities below indicated of the ingredient listed:

Zinc sulphate 48 ounces per gallon of electrolyte.

Ammonium chloride 4 ounces per gallon of electrolyte.

Sodium acetate 2 ounces per gallon of electrolyte.

Dextrose 16 ounces per gallon of electrolyte.

Concentrated sulphuric 1.5 ounces per gallon of acid. electrolyte.

% water solution ti- .8 ounce per gallon of tanous chloride. electrolyte.

10. A method of electroplating zinc on basis metal comprising passing an electroplating current from an anode to the basis metal as a cathode through an electrolyte containing about the quantities below indicated of the ingredients 30% water solution hy- .25 ounce per gallon of drogen peroxide. electrolyte.

11. A method of electroplating zinc on basis metal comprising passing an electroplating current from an anode to the basis metal as a cathode through an electrolyte containing about the quantities below indicated of the ingredients listed:

Zinc sulphate 48 ounces per gallon of electrolyte.

Ammonium chloride 4 ounces per gallon of l electrolyte.

Sodium acetate 2 ounces per gallon of electrolyte.

. Dextrose 16 ounces per gallon of electrolyte.

Concentrated sulphuric 1.5 ounces per gallon of acid. electrolyte.

15% water solution ti- .8 ounce per gallon of tanous chloride. electrolyte.

30% water solution hy- .25 ounce per gallon of drogen peroxide. electrolyte.

at a current density of at least about amperes per square foot.

RAYMOND J. WEAN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,491,381 Classen Apr. 22, 1924 2,233,500 Westbrook Mar. 4, 1941 

1. A METHOD OF ELECTROPLATING A LUSTROUS DUCTILE COATING OF ZINC ON BASIC METAL COMPRISING PASSING AN ELECTROPLATING CURRENT FROM AN ANODE TO THE BASIS METAL AS A CATHODE THROUGH AN ACID ZINC ELECTROLYTE CONTAINING BETWEEN ABOUT .005 AND ABOUT .2 OUNCE OF TITANIUM PER GALLON OF ELECTROLYTE. 